Damn, dude.
I have two coder's cables and a BBA. I
never burn images when I'm trying to test my Dreamcast programs. Especially with all the things I screw up, it's completely unrealistic. I know a bunch of guys who use "multi session" images, so they can burn a million different builds for testing--but even that sucks.
It has been awhile since I've made a selfbooting image, since I've been very much in R&D mode on Dreamcast. I believe you want to compile to a BIN, then convert to scrambled BIN (it might have been unscrambled BIN, I don't remember), then create a selfbooting image. There's a bunch of tools at
http://dcemulation.org for that type of stuff. GCC (your DC compiler) can output the starting binary, since ELF is more of a debug format.
If you're serious about Dreamcast development, you should invest in a better means immediately. "Coder's Cables" connect from your PC serial port to your DC serial port. The only problem is that when you want to test images and audio, the bandwidth is HORRIBLE, so it's slow as hell. If you're VERY serious about it, you should invest in a broadband adapter. They go for about $100 on ebay, but you get a 100mbit connection and can literally stream media for you game/program from your PC to your Dreamcast (as we do with ES).
There are two other alternatives (that I'm not very familiar with). There's a "USB coder's cable" which is the equivalent of the serial, except with a higher bandwidth and using USB. There's also a brand, brand new Dreamcast SD card reader that somebody developed, where you can drag and drop your .ELFs to it and launch them from some SD card launcher.
If you're interested in either of the last two, I can't help you much. Do some research or asking at dcemulation.org. If you are
really serious about Dreamcast development, a broadband adapter is soooo worth the gigantic cost. It makes development a breeze.